Papaalpha, could you point out where your cg is on the wing?
I have a Ka-7 with 4m span, which has the cg about 2 cm behind the LE at the wing root. The overhead view of the wing is about the same as an ASK-13, so I would suspect you should be fine with the cg about 1 cm behind the LE at the wing root (as your span is about half of mine).

The pic on page 9 shows the c o g with a red stripe about 1.5''/37mm behind the leading edge. To have a co g any further forward would mean so much weight in the nose as never to be able to soar let alone even glide on the slope in a light breeze which is always what I aim for and achieved with my same size Blanik and Bocian.

Exactly! Now that's the attitude. MoF, I just rebalanced my Radian again today with a whole new cockpit, pilot, landing gear with skis and recovering the fuselage with 3M packing tape. I thought for sure it was going to be nose heavy. Nope. The extra clear tape on the tail did it. Needed the battery to go more in the nose for proper CoG. Took my time got it to balance level before flying it.

I agree with Scott. Your CG needs to be right, even if it takes more weight than you want. With a light and wrongly balanced model you will not fly at all, with a heavy but well balanced plane you can at least fly, be it faster. Sure it's better to be light, but this is something all pure gliders are dealing with. They miss the natural ballast that's present in the real planes (the fat belly of the pilot in front).

I want and aim for 'dream flyers' that stay up in a light/5mph breeze but also fly perfectly for slow lazy turns and spot landings and yet can cope with 15/18 mph winds.
I am only trying to save some 3ozs of lead in the nose which may add up to only one ounce needed to be saved rear of the c of g.
Always rewarding when everyone else has had no choice but to land and your scale model continues to quietly fly along the slope remaining airborne.

In for a penny,in for a pound so removed top fuselage planking and hacked away at fuselage formers/cross members as much as possible to try and reduce the weight rear of the c o g . Thought about doing such when building and to mention such to StudioRS but was too lazy and polite.
On checking the balance on c o g stand as per pic with no top decking , no extra weight is needed even with the lighter 4 cell battery. The thing is can I put back a lighter decking - maybe of thinner balsa and still achieve this position?

In for a penny,in for a pound so removed top fuselage planking and hacked away at fuselage formers/cross members as much as possible to try and reduce the weight rear of the c o g . Thought about doing such when building and to mention such to StudioRS but was too lazy and polite.
On checking the balance on c o g stand as per pic with no top decking , no extra weight is needed even with the lighter 4 cell battery. The thing is can I put back a lighter decking - maybe of thinner balsa and still achieve this position?

I'm planning to remove ALL the rear decking from F5 back to F10 similar to Chris Williams designed Scheibe-Bergfalke Mü 13 and replace with thin diagonal bracing, then cover with white. Fortunately, I haven't glued in the top sheeting and most the bottom should come off easily. Rudder and and elevator with just be thin ribs and covering.

I doubt if that will give a satisfactory result on an ASK-13. Your fuselage top is round, you will probably not be able to get a nice round finish without the sheeting. On my Ka-7 it worked well without sheeting, but there it's all flat surfaces.

The most important aspects of this build are to fine tune my scratch building skills and make adjustments to the CAD files so the 4 meter ASK-13 can be built sucessfully. The 4 m size will use a different airfoil with more undercamber anyway.

I am kind of proud of the curved balsa sheeting I formed for the rear fuselage and would be a shame to not use this.

All of this building is all fun anyway, totally enjoying this as I go along. If it flys, great! if it needs loads of wieght, oh well I'll save it for my Cape Cod slope soaring fleet.

I doubt if that will give a satisfactory result on an ASK-13. Your fuselage top is round, you will probably not be able to get a nice round finish without the sheeting. On my Ka-7 it worked well without sheeting, but there it's all flat surfaces.

Right, I meant to say that I will be removing all of the sheeting from F5 below the curved top deck line.